1. Field of the Invention
This invention relates to a preserving material and a method for producing the same. More particularly, the invention relates to a preserving material which can maintain the freshness of foodstuff or the like avoiding the deterioration of them. The preserving material of the present invention is characterized in that it can be conveniently sealed into packages of foodstuffs and the like to be preserved and the preserving liquid contained in the preserving material is not brought into direct contact with substances to be preserved in packages.
Furthermore, the present invention relates to a method for producing a preserving material inexpensively in a continuous manner. The component layers of the preserving material are well bonded together and hardly peeled off.
2. Description of the Prior Art
It has been well known that ethyl alcohol is useful for sterilizing or for inhibiting the growth of microorganisms in order to preserve foodstuffs such as bread, fish, meat, fruits and vegetables.
For example, it is disclosed in Japanese Patent Publication No. 55-1787 that ethanol is directly sprayed to the surface of foodstuffs. Similar methods to use ethanol are disclosed also in U.S. Pat. No. 3,908,031 and Canadian Patent No. 699,278.
In these methods, however, even though the effect of preservation is good, they are not desirable in view of external appearance and commercial value of foodstuffs because the natural good quality of foodstuff is lost and flavors and coloring agents sometimes ooze out owing to the process that foodstuffs are applied with a thin layer of alcohol.
In Japanese Patent Publication No. 40-25228 and No. 55-2273, it is disclosed that ethanol is adsorbed by an adsorbent composed of the powders of starch, dextrin, gelatin, cellulose, silicon dioxide, aluminum silicate and talc and it is sealed together with a foodstuff in a gastight container.
In this method, however, because the bulky adsorbent powders such as starch and silicon dioxide are used and the surface areas of powders are very large, the rate of evaporation of the adsorbed alcohol is too large. Therefore, the effect of preservation cannot be maintained for a long period of time.
That is, in the case that the evaporation of alcohol from an adsorbent is too large, it is necessary that foodstuff packing is carried out soon after the adsorption of alcohol by an adsorbent, which causes difficulties in packing process. Because the leakage of alcohol gas from packages of foodstuffs cannot be avoided completely, a long time preserving effect is not produced when packages are not replenished with alcohol. In other words, in order to maintain the concentration of alcohol above a certain level, it is preferable that the evaporation of alcohol controlled and reduced to a lower rate.
Furthermore, when foodstuffs are preserved using these ethanol-carrying powder, a bag or other container to hold the powder is inevitable, so that the process for packing foodstuff is complicated which increases the packing cost. In addition, if the container of the adsorbent powder happen to break down, the foodstuff in the package is contaminated with the adsorbent powder.
Besides the foregoing ones, there are many other references with regard to the use of preserving agents. For the purpose of information, some references are listed below. It is to be noted, however, that the references do not relate directly to the present invention because the present invention is not intended to provide any preserving agent itself but to propose a novel preserving material of layered structure and a method for producing the same.
a) Preservation of foodstuffs using ethanol and organic acids or their esters:
Japanese Patent Publication No. 50-25531, No. 52-27217, No. 53-28485, No. 55-01787, No. 55-02274, No. 55-50674, No. 58-49156 and No. 58-49157, and U.S. Pat. No. 4,550,026.
b) Preservation using ethanol and deoxidizing agents.
Japanese Patent Publication No. 57-79869, No. 57-079870 and No. 60-70053.
c) Preservation using ethanol in solid form:
Japanese Patent Publication No. 60-184374, No. 62-69971 and No. 62-232365.
d) Preservation using deoxidizing agents:
Japanese Patent Publication No. 48-11026, No. 50-04740, No. 51-34898, No. 53-33665, No. 55-44594, No. 57-18787, No. 58-29069, No. 59-32106, No. 60-30503, No. 60-30504, No. 60-31465, No. 60-35102, No. 60-36747, No. 61-17463, No. 61-36912, No. 61-36913 and No. 61-36914.
e) Preservation using other agents:
British Patent No. 1,277,874 (propionic acid), U.S. Pat. No. 3,346,398 (alkylene oxides), U.S. Pat. No. 3,533,806 (carbon tetrachlrride and glacial acetic acid), U.S. Pat. No. 3,600,198 (propionic acid and benzoic acid), U.S. Pat. No. 3,595,665 (acetic, propionic and formic acids), U.S. Pat. Nos. 4,350,709 and 4,421,774 (sulfur dioxide, organic acid such as propionic acid and ammonia gas), U.S. Pat. No. 4,356,204 (ketohexanoic acids), U.S. Pat. No. 4,404,340 (C.sub.6 -C.sub.14 fatty acids), U.S. Pat. No. 32,416 (acid propionate salt), Australian Patent No. 102,824 (C.sub.3 -C.sub.12 saturated aliphatic monocarboxylic acids) and Austalian Patent No. 110,824 (halogenated hydrocarbon containing dichloromethyl group).
Conventionally known methods have several disadvantages in that some methods deprive foodstuffs of natural quality or flavor; they spoil external appearance of foodstuffs the effect of preservation cannot be maintained for a long period of time; absorbent or adsorbent material and gastight container are required; and as mentioned in the foregoing paragraphs, the process for the package of foodstuffs cannot be easy and simple and foodstuffs are liable to be contaminated by preserving agents.